<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Fixed-Width Sidebar</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            min-height: 100vh;
            display: flex;
            flex-direction: column;
        }

        header,footer{
            height: 60px;
            line-height: 60px;
            background: #0f5aff;
        }

        .content{
            display: flex;
            flex: auto;
        }

        aside{
            flex: 0 0 200px;
            background: lawngreen;
        }
        section{
            flex: auto;
        }
    </style>
</head>
<body>

<header>header</header>
<div class="content">
    <aside>aside</aside>
    <section>content</section>
</div>
<footer>footer</footer>

</body>
</html>
